Motivational vs. motor effects of striatal and pallidal gabergic projections to subthalamic and entopeduncular nuclei, ventromedial thalamus, and ventral globus pallidus.

Four GABA-terminal sites downstream from the rat corpus striatum were injected bilaterally with either a GABA agonist (muscimol 15-250 ng) or antagonist (picrotoxin 15-300 ng), and the effects on spontaneous locomotor activity or variable-interval hypothalamic self-stimulation were recorded. Significant changes in locomotor activity were produced at all four sites, as in previous studies. Two of the sites tested, the anterior globus pallidus and the thalamic ventromedial nucleus, also receive gabergic projections from the nucleus accumbens or from structures other than the basal ganglia; at these two sites, injection of either muscimol (depressant), or picrotoxin (facilitatory), had the same effect on self-stimulation as on locomotor activity. The two other sites tested, the entopeduncular nucleus and subthalamic nucleus, do not receive projections from the accumbens; in these two structures, muscimol enhanced locomotor activity but abolished self-stimulation; picrotoxin was without significant effect, or was disruptive. These results confirm previous reports that gabergic systems downstream from the striatum can mediate a simple, innate motor sequence (locomotion), but they fail to demonstrate a specific involvement of these pathways in learned behaviour (self-stimulation).